1. Field of the Invention
The present invention relates to a roller cage made of metal for holding a roller of a roller bearing and, more particularly, relates to the technique for, at the time of press-molding a contact surface contacting to the rolling surface of the roller at the peripheral portion of a window hole for receiving the roller, performing the press-molding so as not to degrade the accuracy of the size of the roller cage.
2. Description of the Related Art
Conventionally, various types of roller bearings have been employed, and some of them employ a roller cage which is formed by press-molding a metal plate of steel plate or the like.
An example of such a roller cage made of metal will be explained with reference to FIG. 11. A roller cage 1 includes a plurality of window holes 2 for receiving a plurality of rollers respectively, a pair of front and rear flange portions 3, 4 for sandwiching the window holes 2 along the direction of the rotational axis of the roller bearing, and a plurality of separation bars 5 for separating the window holes along the rotational direction of the roller bearing. The roller cage 1 serves to hold a plurality of rollers 8, which roll while being in contact with an inner ring 6 and an outer ring 7 of the roller bearing, along the rotational direction of the roller bearing with a constant interval thereamong, as shown in FIG. 12.
As shown in FIG. 12, each of the separation bars 5 is provided with contact surfaces 9 contacting with the rolling surfaces of the adjacent rollers 8 at the peripheral portions of the adjacent window holes on the upper surface Sa side of the each separation bar 5. Each of the contact surfaces 9 is formed as schematically shown in FIG. 13 in a manner that the side surfaces 10, which are formed at the time of forming the corresponding one of window holes 2 by the stamp-molding process, are subjected to the press-molding by using a pressing die 11 and a backing (supporting) die 12 to press to the vertical direction in the figure thereby to form the contact surfaces. Accordingly, since the contact surfaces 9 can be made smooth, such a problem can be surely prevented that the abrasion is caused on the rolling surface of the roller 8.
At the time of subjecting the contact surfaces 9 of the roller cage 1 to the press-molding, the roller cage is pressed from a direction perpendicular to the axial direction thereof regardless of the type of the roller cage. When the pressing die 11 presses the upper surface side peripheral portions 10a of the window holes 2, portions (sectional areas) shown by a symbol S0 in FIG. 13 are pressed and simultaneously portions (sectional areas) shown by symbols S1 and S2 in FIG. 13 expand.
However, in the related press-molding method for the roller cage 1, since the backing die 12 supports the entirety of the lower surface Sb of the separation bar 5, the separation bar 5 can not be freely deformed at the time of the press-molding.
Thus, since the sum (S1+S2) of the increments of the sectional areas of the separation bar 5 is smaller than the decrement (S0) of the sectional area thereof, the separation bar 5 extends to an elongated direction of the separation bar in order to compensate the decrease of the sectional area. As a result, the accuracy of the size of the roller bearing degrades.
Thus, in the related art, in order to reduce the amount of the expansion of the separation bar 5 caused at the time of press-molding the contact surface 9, there have been employed such a method that the stroke of the pressing die 11 is reduced thereby to make the area of the contact surface 9 narrower, or that the size of the separation bar is set in view of the expansion of the separation bar 5. However, in each of such related methods, the number of required press-molding processes becomes quite large.
Further, in the related art, since it is difficult to manage the accuracy of the size of the roller cage, there has been a demand for the press-molding technique which can process a roller cage without degrading the accuracy of the size thereof.